A device for detecting an electric current with a Hall effect sensor is known for example by Japanese Patent Disclosure No. 1-145837. The detecting device comprises a support pad, a plurality of lead terminals mounded around the support pad, a Hall effect sensor attached on a main surface of the support pad, wires for electrically connecting electrodes and lead terminals, and a plastic package for sealing the Hall effect sensor, wires, support pad and each inner end of the lead terminals. Flow of electric current through an object produces a magnetic field normal to the flowing direction of the electric current in the object, and placement of the detecting device in the magnetic field establishes a potential difference in the Hall effect sensor due to the Hall effect because the Hall effect sensor converts the magnetic field into electric voltage to detect or measure the current flow value. This potential difference is known as the Hall voltage perpendicular to the directions of the electric current and magnetic field, and the Hall voltage is proportional to the value of the detected electric current through the object.
Meanwhile, a current detector of another type has been proposed wherein a plastic package covers a Hall element positioned in a through hole formed in the package. This current detector includes a conductor inserted into the through hole to pass electric current through the conductor. Since the Hall element is disposed in the vicinity of the conductor, it can directly detect the current flow running through the conductor with good sensitivity. In this current detector, however, a problem arises that it requires troublesome and complicated assembling processes for inserting the conductor such as a wire into the through hole in the plastic package at a predetermined height, and thereby the assembling process impedes the changeover to automation of assembling process for the detectors. To overcome this problem, a new structure of the current detector has been developed as shown by “Alllegro Current Sensor, ACS750” presented by Allegro MicroSystems Inc., Worcester, Mass. (http://www.allegromicro.com/datafile/0750.pdf>). This detector utilizes an integrated packaging structure with a plastic package for encapsulating or molding a Hall effect sensor and a conductor into one piece to attain a stable current detection because the conductor provides a fixed current path relative to the Hall effect sensor in the package.
However, a large electric current flowing through the conductor heats the conductor to thereby cause heat and thermal stress exerted on the Hall effect sensor in the package so that there is a likelihood of deterioration of electric property in the Hall effect sensor and degradation of mechanical property in the plastic package. Also, the conductor requires its high machining accuracy enough to mount the current detector in position on a surface of a substrate keeping the conductor at a same level as lead terminals, thus lowering the productivity and yield.
Accordingly, an object of the present invention is to provide an electric current detector capable of restraining deterioration of electric property in a Hall effect sensor and degradation of mechanical property in a plastic package although a large electric current flowing through the conductor produces heat and heat stress in a conductor.
Also, another object of the present invention is to provide an electric current detector that can be mounted in position on a surface of a substrate with the conductor retained at the same level as lead terminals without high machining accuracy.
Still another object of the present invention is to provide an electric current detector capable of detecting a large electric current flowing through the conductor with high accuracy.